Pipe Dreams: Advances In Cable Jetting

For many years, cable technicians have used
“air jetting” (cable blowing) to install fiber
optic cable over great distances in long-haul
applications. The process involves using
compressed air (or nitrogen gas) to propel
the cable through pipe-like structures called
innerducts.

Cable jetting works well in long-haul
applications because the cable is installed
in a relatively straight line, typically within
buried cable ducts. In premise environments,
cable jetting is more challenging because of
bends and curves in the cable run. Also, most
buildings and campuses don’t yet have the
required ductwork in place.

Nonetheless, many network operators dream
of the day when cable jetting can be used
to more easily install fiber within premise
environments. This article highlights recent
advancements that promise to make these
“pipe dreams” a reality.

TRADITIONAL INSTALLATION METHOD

Installing fiber optic cable within
a building or campus traditionally
involves “pulling” cable. The
process begins by sending a
pull line through a cable duct
or other available pathway. The
cable is then attached to the line
and pulled into place manually
or by mechanical means. Some
cable ducts come with pull lines
preinstalled.

One of the problems with cable
pulling is that it forces the cable
to be pulled tightly against the
surface of every inside curve in the
cable run. This greatly increases
resistance on the cable and limits
the distance over which it can
be pulled. The process also risks
damaging the cable because more
pulling force is required as the
cable pull progresses. The problem
is the same whether the cable is
installed in metal conduit or run
through wooden wall studs.

Getting Your Ducts in Order

There are various types of
ducts and conduits used in cable
jetting, some of which have
similar-sounding names.
To avoid confusion, it is
important to understand the
difference between Innerducts,
Microducts and Conduits.

Innerducts are designed for Air
Blown Cable (ABC) applications
that involve jetting relatively thick
fiber optic cable. Innerducts are
often placed inside larger cable
pathways such as Conduits, which
may hold other types of cabling.
Note that innerducts have been
used for cable pulling for decades.
However, these older corrugated
innerducts are not well suited
for cable jetting, unless they are
retrofitted with newer innerducts
and/or microducts specifically
designed for cable jetting.

Microducts are used in Air Blown
Fiber (ABF) applications for
jetting small diameter micro cable
and “loose tube” fibers. Microducts
can be installed within innerduct
or purchased as a self-contained
“sheathed microduct
bundle” (below).

CABLE PULLING VS. JETTING

In contrast to pulling, cable jetting
typically employs a pushing
mechanism, such as capstans,
in conjunction with compressed
air to move the cable through a
dedicated cable duct. Because
there is little or no pulling involved
there is less resistance to the cable
as it is installed around curves.
In some cases a blowing tip is
attached to assist in the installation
of the cable.

Cable Jetting Benefits

REDUCED COST
After the initial cost of ductwork
and equipment (which can be
amortized), fiber upgrades can
result in savings of up to 90%.
Cable jetting requires fewer
installers and reduces the number
of splices, manholes, handholes
and access points required.

LONGER DISTANCE
Cable can be jetted 4,000 feet or
more between jetting locations.
Typically, pulled cable can be
installed over a maximum distance
of only 600 feet between pulling
locations.

FASTER INSTALLATION
Jetted fiber can be installed at
speeds of 200 feet per minute.
Typically, pulled fiber can be
installed at a rate of only 100 feet
per minute.

LESS-DISRUPTIVE
With cable jetting, fiber upgrades can be accomplished without disrupting the workplace.

ELIMINATES DARK FIBER
When installing ductwork forjetting, some microducts can be left empty to accommodate new fiber when required. This eliminates the need to install dark fiber, which can become obsolete.

BETTER CABLE PROTECTION
Cable jetting requires that fiber optic cables be installed within their own cable ducts. After jetting, the cables remain in the ducts,which affords continued
protection for the fiber.

ELIMINATES ORPHANED FIBER
Cable installed by traditional methods can be difficult or impossible to remove. Old cable is typically abandoned in place, which takes up valuable space in cable pathways. In contrast, fiber installed by cable jetting is easy to remove by using the same jetting process that installed it. The removal process is relatively gentle, so the extracted fiber can often be used in other applications.

SLICK SOLUTIONS

Recent advances in materials and equipment are making cable jetting a viable solution for installing fiber optic cable in premise environments.

‘SLIPPERY’ INNERDUCT
New cable lubricants are available that are made specifically for cable jetting. Some ducts have low friction materials embedded within the interior wall of the duct.

DUCT GEOMETRY
Ducts are available with special ribbing and other surface features
that reduce drag by minimizingcontact between the cable
and the duct.

STANDARDS COMPLIANT
Many of the new ducts are made of high density polyethylene (HDPE), offer low-smoke zero-halogen options, and are available with riser and/or plenum ratings.

SPECIALIZED CABLE
Almost any type of fiber optic cable can be jetted. However, cables that are too stiff require more force to carry them through bends in the cable path. If cables are too flexible, the capstans pushing the cable may cause them to bunch up. To ensure success, use cables that are made for cable jetting.

THINNER OPTICAL FIBER
Optical fibers are now available that have thinner cladding, which greatly reduces the diameter of the fiber. Thinner fiber increases the number of fibers that can be installed in a given innerduct, and provides cable with more flexibility to negotiate curves and bends.

Cable Jetting Applications

Today, cable jetting can be used almost anywhere conventional fiber is deployed, including:

NEW CABLE JACKETS
Some cables designed for cable jetting have a rough or textured jacket that enables jetted air to better “grip” and propel the cable.

COMPACT JETTING EQUIPMENT
Compared to traditional jetting equipment, new equipment designed for premise applications is easier to use, less expensive and less intrusive in the workplace.

LET US KNOW WHAT YOU THINK

Not everyone agrees that cable
jetting is a better alternative to
cable pulling for premise
applications. Detractors point out
that cable jetting standards
haven’t yet been fully developed,
the jetting process is relatively
complex, and there are significant
upfront costs for jetting equipment
and ductwork.
In reply, advocates of cable jetting
say these costs can be amortized,
and that the future savings
afforded by cable jetting are far
greater than the upfront costs.